The present invention relates to computer storage systems and, more specifically, to protecting former primary volumes in a synchronous replication relationship.
High-reliability storage systems typically use data replication to maintain a secondary copy of data stored in a primary volume. A systems complex, also referred to as a sysplex, is an example of a high-reliability system that allows multiple logical partitions to communicate and coordinate synchronized data storage and access for large-scale data storage and management. A parallel sysplex provides data sharing capabilities for accessing multiple databases to read and write as shared data. System members are synchronized using timers and a coupling facility for data sharing. A geographically dispersed parallel sysplex (GDPS*) environment enables a parallel sysplex to be at geographically separate sites while maintaining coordinated data system management; however, the GDPS environment need not be geographically separated. A GDPS environment in combination with peer-to-peer remote copy (GDPS/PPRC) enables synchronous data mirroring using PPRC volume pairs (i.e., primary and secondary volumes) for systems that can be separated by substantial distances, e.g., 120 miles. PPRC is an example of a synchronous replication technology. In a two system configuration, GDPS/PPRC allows the systems at separate sites to be administered as a single system. In the event of a system or storage device failure, recovery can be initiated automatically with minimal or no data loss.
Swapping between primary and secondary volumes can be performed using various support features in a high-reliability storage system. A HyperSwap* operation in a GDPS system is one example of a swapping function. The HyperSwap operation can help significantly reduce the time needed to switch to secondary PPRC volumes (i.e., a mirrored set of disks) that hold a copy of data from primary PPRC volumes while keeping the underlying operating system active together with associated applications. A HyperSwap manager automates the process of making the secondary PPRC volumes become the primary PPRC volumes with minimal to no disruption to applications running in the GDPS system. In a HyperSwap environment when there is an error that triggers an unplanned HyperSwap operation, the GDPS system will typically perform the HyperSwap operation in all of the members of the sysplex. After the HyperSwap operation there are several exposures to system images using the former primary PPRC volumes. For a planned or unplanned HyperSwap operation, PPRC pairs can be reestablished in the reverse direction using a PPRC failover function. This can result in the former primary PPRC volumes remaining accessible. For example, any system accessing the former primary PPRC volumes will read data that could be stale, and any updates to the former primary PPRC volumes will be lost when the PPRC pairs are reestablished in the reverse direction. (* GDPS and HyperSwap are trademarks or registered trademarks of International Business Machines Corporation.)